[PATCH] 2.4.19-pre8 vm86 smp locking fix

[PATCH] 2.4.19-pre8 vm86 smp locking fix

[Benjamin LaHaise]

arch/i386/kernel/vm86.c performs page table operations without obtaining 
any locks.  This patch obtains page_table_lock around the the table walk 
and modification.

		-ben
-- 
"You will be reincarnated as a toad; and you will be much happier."


diff -urN v2.4.19-pre8/arch/i386/kernel/vm86.c work/arch/i386/kernel/vm86.c
--- v2.4.19-pre8/arch/i386/kernel/vm86.c	Thu Mar  7 16:39:56 2002
+++ work/arch/i386/kernel/vm86.c	Thu May 23 16:21:38 2002
@@ -97,21 +97,22 @@
 	pte_t *pte;
 	int i;
 
+	spin_lock(&tsk->mm->page_table_lock);
 	pgd = pgd_offset(tsk->mm, 0xA0000);
 	if (pgd_none(*pgd))
-		return;
+		goto out;
 	if (pgd_bad(*pgd)) {
 		pgd_ERROR(*pgd);
 		pgd_clear(pgd);
-		return;
+		goto out;
 	}
 	pmd = pmd_offset(pgd, 0xA0000);
 	if (pmd_none(*pmd))
-		return;
+		goto out;
 	if (pmd_bad(*pmd)) {
 		pmd_ERROR(*pmd);
 		pmd_clear(pmd);
-		return;
+		goto out;
 	}
 	pte = pte_offset(pmd, 0xA0000);
 	for (i = 0; i < 32; i++) {
@@ -119,6 +120,8 @@
 			set_pte(pte, pte_wrprotect(*pte));
 		pte++;
 	}
+out:
+	spin_unlock(&tsk->mm->page_table_lock);
 	flush_tlb();
 }
 

Re: [PATCH] 2.4.19-pre8 vm86 smp locking fix

[Kasper Dupont]

Benjamin LaHaise wrote:
> 
> arch/i386/kernel/vm86.c performs page table operations without obtaining
> any locks.  This patch obtains page_table_lock around the the table walk
> and modification.

This patch can also be applied against 2.4.19-pre8-ac5.
The patch command does report:
patching file arch/i386/kernel/vm86.c
Hunk #1 succeeded at 124 (offset 27 lines).

Since this missing lock is completely unrelated to the
other bugfixes in vm86 I don't expect any bad interactions.

The pagetable access in arch/i386/kernel/vm86.c is related
to another access in arch/i386/mm/fault.c. Did anybody
verify that the other file does correct locking?

-- 
Kasper Dupont -- der bruger for meget tid på usenet.
For sending spam use mailto:razor-report@daimi.au.dk

Re: [PATCH] 2.4.19-pre8 vm86 smp locking fix

[Benjamin LaHaise]

On Thu, May 23, 2002 at 11:36:23PM +0200, Kasper Dupont wrote:
> The pagetable access in arch/i386/kernel/vm86.c is related
> to another access in arch/i386/mm/fault.c. Did anybody
> verify that the other file does correct locking?

That should be safe: the vmalloc pgds can only be filled from the 
main kernel page table.  They never change afterwards, so even if 
two CPUs entered that code at the same time it would be okay.

		-ben
-- 
"You will be reincarnated as a toad; and you will be much happier."